Method and Device for Generating Control Words

Abstract

The present invention relates to the generation of n control words for encryption of a content item. A device obtains a first key K start and a second key K end ; generates the n control words using the formula: CW i =h 1 i (K start ) ⊕h 2 n-i (K End ), i=0 . . . n−1, wherein CW i denotes 5 control word i, h 1 and h 2 denote one-way functions, and ⊕ denotes a combination operation; and outputs the n generated control words. The least one one-way function is preferably a hash function and the combination operation is preferably XOR.

1 . A device for generating n control words for encryption or decryption of n contiguous units of a content item, wherein n is an integer, the device comprising a processor configured to:
 obtain a first key K start  and a second key K end ;   generate a first ordered set of n subkeys K 1   0 −K 1   n-1  by iteratively applying a first one-way function to the first key K start  and a second ordered set of n subkeys K 2   0 −K 2   n-1  by iteratively applying a second one-way function to the second key K end ;   generate n control words by iteratively using a combination operation to generate control word i from subkey K 1   i  from the first ordered set of n subkeys and subkey K 2   n-i-1  from the second ordered set of n subkeys, wherein 0≦i≦n−1; and   output the n generated control words.   
     
     
         2 . The device of  claim 1 , wherein at least one of the first one-way function and the second one-way function is a hash function. 
     
     
         3 . The device of  claim 1 , wherein at least one of the first one-way function and the second one-way function is public key encryption. 
     
     
         4 . The device of  claim 1 , wherein the combination operation is XOR. 
     
     
         5 . The device of  claim 1 , wherein the combination operation is concatenation or public key encryption or symmetric key encryption. 
     
     
         6 . The device of  claim 1 , wherein the processor is further configured to separate the content item into a plurality of parts, each part comprising a plurality of units; and to generate control words independently for each part. 
     
     
         7 . The device of  claim 1 , wherein the processor is further configured to:
 generate a license for the content item of which unit i has been encrypted using generated control word i, the license comprising the first key K start , the second key K end  and the integer n; and   transmit the license to a receiver.   
     
     
         8 . The device of  claim 7 , wherein the content item is an excerpt of a longer content item, the longer content item being encrypted using control words generated from a third key and a fourth key, and wherein the processor is further configured to:
 generate the first key K start  by iterative application of the first one-way function to the third key; and   generate the second key K end  by iterative application of the second one-way function to the fourth key.   
     
     
         9 . The device of  claim 1 , wherein the content item is encrypted and the processor is further configured to decrypt the encrypted content item using the generated control words. 
     
     
         10 . A method for generating n control words for encryption or decryption of n contiguous units of a content item, wherein n is an integer, the method comprising, at a device, the steps of:
 obtaining a first key K start  and a second key K end ;   generating a first ordered set of n subkeys K 1   0 −K 1   n-1  by iteratively applying a first one-way function to the first key K start  and a second ordered set of n subkeys K 2   0 −K 2   n-1  by iteratively applying a second one-way function to the second key K end ;   generating n control words by iteratively using a combination operation to generate control word i from subkey K 1 , from the first ordered set of n subkeys and subkey K 2   n-i-1  from the second ordered set of n subkeys, wherein 0≦i≦n−1; and   outputting the n generated control words.   
     
     
         11 . The method of  claim 10 , wherein at least one of the first one-way function and the second one-way function is a hash function. 
     
     
         12 . The method of  claim 10 , wherein the combination operation is XOR. 
     
     
         13 . The method of  claim 1 , further comprising the step of separating the content item into a plurality of parts, each part comprising a plurality of units; and wherein the steps of  claim 10  are performed independently for each part. 
     
     
         14 . A method of generating a content license for a content item being encrypted using control words generated by the method of  claim 10 , the method comprising, at a device, the steps of:
 generating a license for the content item of which unit i has been encrypted using generated control word i, the license comprising the first key K start , the second key K end  and the integer n; and   transmitting the license to a receiver.   
     
     
         15 . The method of  claim 14 , wherein the content item is an excerpt of a longer content item, the longer content item being encrypted using control words generated from a third key and a fourth key, and wherein the method further comprises the steps of:
 generating the first key K start  by iterative application of the first one-way function to the third key; and   generating the second key K end  by iterative application of the second one-way function to the fourth key.